(i) Field of the Invention
The present invention relates to a lighting apparatus of an edge light type used for backlighting of a light receiving type liquid crystal display device.
(ii) Description of the Prior Art
In the past, various types of lighting apparatus, used in liquid crystal display devices have already been proposed, including many known apparatuses of a so-called edge light type, disclosed in Japanese Patent Publication No. Sho 54-18886 and Japanese Patent Application Laid-Open No. Hei 3-171009. In these apparatuses wherein light sources are disposed at opposite ends of an optical conductor, and backlighting of the display device is effected indirectly through the optical conductor. Another known apparatus is a so-called backlighting type, disclosed in Japanese Patent Application Laid-open No. Sho 64-987, wherein a light source is disposed directly at the back of an optical conductor. Of these types, the device using a lighting apparatus of the edge light type is advantageous in that the whole display device can be reduced in thickness.
As shown in FIGS. 1 to 3, in the conventional lighting apparatus of the edge light type used for a liquid crystal display device, lamps such as cold cathode tubes or hot cathode tubes are used as light sources 1. The light sources 1 are disposed at opposite ends of an optical conductor 2 made of a transparent material. Further, a diffusion sheet 3, having a light scattering capability for the sake of making the brightness over the entire illuminating plane uniform, is formed as a milk-white, synthetic resin plate on the top surface of the optical conductor 2. Finally, a mirror reflector or a light scattering acrylic plate is used as a reflector sheet 4. The reflector sheet 4 is adapted to improve the utilization efficiency of light by reflecting light, emitted from the light sources and heading toward the back side, toward the front side.
As shown in FIG. 2, a laminated plate of three layers of the diffusion sheet 3, optical conductor 2 and reflector sheet 4 is clamped and held through its front and back surfaces by a window frame 5 and a support 6 (chassis) fitted to the back of the window frame 5 by screws.
In the Figures, reference character 7 designates light source reflectors for reflecting light, emitted from the light sources and heading toward the outside, back toward the optical conductor 2. Further, X is a liquid crystal display panel, L1 is an effective illuminating area of the light sources 1 and L2 is an effective display area of the liquid crystal display panel X.
In the conventional liquid crystal lighting apparatus, however, the laminated plate of layers of the diffusion sheet 3, optical conductor 2, reflector sheet 4 and light source reflector 7 are overlaid through its front and back with the window frame 5 and the support 6 as shown in FIGS. 2 and 3. Therefore the thickness dimension of the whole liquid crystal lighting apparatus is increased. For example, when thickness dimensions of individual members are exemplified such that the optical conductor has a thickness of 5.0 mm, the diffusion sheet 3 has a thickness of 0.25 mm, the reflector sheet has a thickness of 0.18 mm, the support has a thickness of 0.5 mm and the light source reflector 7 has a thickness of 0.1 mm, a portion shown in FIG. 2 has a thickness of 5.93 mm as measured from the front surface of the window frame 5 and a portion shown in FIG. 3 has a thickness of 6.13 mm as measured from the front surface of the window frame 5. If the thickness of the optical conductor 2 is reduced to accomplish thickness reduction for the whole apparatus, the area of the light incident end surfaces, through which light from the light sources 1 goes into the optical conductor, is decreased correspondingly. Thus, difficulties have arisen in attempting to satisfy the trade-off between the thickness reduction and the realization of high brightness of the liquid crystal lighting apparatus.